1. Field of the Invention
The present invention relates generally to a main direct access storage device (DASD) and pertains particularly to a novel arrangement of a DASD interconnected via an electronic control system to an embedded smaller sized supplementary DASD in order to enhance performance, functionality, efficiency, and reliability.
2. Discussion of the Related Art
One of the principle components of a computer system is a memory device or other place to store data. Typically computer systems employ a number of storage means for storing and retrieving data used by the computer. For example, a computer system can store data in a peripheral storage device referred to as a disk drive or direct access storage device (DASD).
Generally, a DASD comprises at least one rotating disk covered with a magnetic coating which can store magnetic or electronic data; or a disk including an optically encoded medium; and an apparatus for reading data from and writing data to that disk. Typically, the apparatus for reading and writing data includes a xe2x80x9cspindle motorxe2x80x9d to rotate the disk, at least one xe2x80x9cread/write headxe2x80x9d to read and write data to and from the disk, an xe2x80x9cactuatorxe2x80x9d to position the read/write head or heads radially over the disk, and a xe2x80x9cdata channelxe2x80x9d to transfer information between the read/write head or heads and an accessing source. An electronic system controls the rotating disk, spindle, heads, and transfer of information to and from the disk and the rest of the computer system. Finally, a computer interface, for example, the standardized Small Computer Synchronous Interface (SCSI), is used to interface the DASD with the rest of the computer.
Today""s technology relating to data storage and DASDs is marked by continuing trends towards standardization and towards increased storage capacity, increased read and write speeds, reduced data storage device weight and size, and reduced power consumption. Standardization in size, referred to as form factor, and in interface compatibility is being pursued by manufacturers of both desktop systems such as personal computer (PC) and workstation systems and larger computing systems. Thus, DASDs from several different manufacturers, having differing capabilities and capacities, but with standard form factors and plug-in configurations may be used interchangeably in different PC""s, for example, in standardized plug-in slots provided by the PC manufacturers.
These plug-in configurations have lead to electronic system designs employing multiple DASDs to increase storage capacity, reliability, and data throughput. For example, data throughput has been increased by reducing the time required to record or reproduce data (access time) by organizing multiple DASDs in a redundant array of independent disks or RAID array. A controller accesses stripes of parallel data across the multiple disks in the array to achieve higher data transfer rates by filling the data gap that results when one DASD is unavailable for reading data, or is seeking a new data segment, with a stripe of data from another DASD.
Various techniques such as those in U.S. Pat. No. 5,398,158, Japanese Patent No. JP 5325496, and JP 06084338A have been proposed in order to implement redundant array of independent disks (RAID) technology. However, these proposals teach an array of similar sized disks, each mounted separately and connected only through external interface cables to a central disk or controller. Thus, as further explained below, these configurations are less efficient, have slower data throughput, have inferior error logging, and require more space than the present invention because they involve multiple similar type disks mounted separately and connected via external interfaces. Another proposal, U.S. Pat. No. 5,422,767, assigned to the assignee hereof, offers multiple independent disks mounted on a base having a vibration damper. Again, this set up will not be as efficient, quick, or small as the current device because it also teaches multiple similar type disks mounted separately and connected via external interfaces.
However, these prior systems are hampered by the use of multiple independent disk drive units which do not fit within the form factor of a single drive. Further, these systems are complicated because each independent drive has its own control circuitry and is connected through a standard interface to a separate controller or controlling disk drive. Additionally, these systems suffer from a limited capacity semiconductor or chip based volatile cache memory which looses its data (volatile) every time it is cleared, written over, powered down, or fails. Finally, because the error log for each DASDs is kept on the disk itself, the log is limited in detail and often unrecoverable (volatile).
Therefore, there exists a need for a DASD that has increased non-volatile cache memory, extensive non-volatile error logging capacity, increased parallel data access, increased data throughput during RAID operation, and read/write capability prior to main disk spin up; and that fits within a standard disk drive form factor.
It is a primary object of the present invention to provide an improved DASD that has increased non-volatile cache memory, extensive non-volatile error logging capacity, increased parallel data access, increased data throughput during RAID operation, and read/write capability prior to main disk spin up; and that fits within a standard disk drive form factor
The present invention solves the problem of DASD limited and volatile caches; limited and volatile error logs; lack of parallel data access; lack of data transfer prior to DASD spin-up; and inefficient operation during RAID operations. Broadly, the present invention provides an enhanced and superior DASD with increased performance, functionality, efficiency, and reliability.
In accordance with a primary aspect of the present invention, a digital access storage device has a main first disk drive, at least one second smaller disk drive, and an electronic control system interconnecting the disk drives. In a preferred embodiment, the first and second disk drives may be physically mounted on a common chassis.
However, the claims alonexe2x80x94not the preceding summaryxe2x80x94define the invention.